The present invention relates to mining and construction cutting bits and holders, the holders being attached to a rotating cutting drum. In the past, rotatable cutting tools have been put to a number of uses, including use as a mine tool in a continuous mining machine. Typically, a continuous mining machine includes a driven rotatable drum having a plurality of support blocks affixed thereto.
The invention concerns a rotatable cutting bit, as well as the bit holder, wherein the cutting bit has a hard insert at the forward end thereof. The cutting bit rotatably mounts in the bit holder. More specifically, the invention pertains to such a rotatable cutting bit, as well as the bit holder, designed so as to exhibit a reduction in the impediment to rotation, and thereby provide for improved rotation, between the bit and the bit holder. The invention also provides for a rotatable cutting bit, as well as the bit holder, which provides for improved wear protection for the bit holder during operation.
In the prior art, such as U.S. Pat. No. 6,113,195, to Mercier et al., and U.S. Pat. No. 4,818,027, to Simon, the bit block holder is protected from wear caused by rotation of the cutter bit head and shank by a holding washer element and spring sleeve retainer respectively. In the cutter bit provided with the holding washer element, the clamping sleeve is held tightly enough that the cutter bit with the clamping sleeve can be pushed into the bore of the bit holder even manually over a great portion of its axial dimension, until, for example, the holding element abuts on the insertion side of the bit holder. The cutter bit can be driven to the shoulder of the bit head adjacent the bit holder by means of a hammer blow. By this means, the holding element is slid from the clamping sleeve, and reaches an area of the bit shank free from the clamping sleeve, so that the clamping sleeve, with the clamping force particular to it, can be tensed in the bore of the bit holder, whereby the tension force correspondingly increases with increasing drive-in depth.
In operation, the drum rotated whereby the rotatable cutting tools impacted the earth formation, such as, for example, coal, so as to cut and break up the earth formation. As can be appreciated, the earlier rotatable cutting bits operated in an environment in which small particles of the earth formation impacted by the bit, such as coal, impinged upon the cutting bit. As the length of operation increased, these contaminants or debris had the tendency to become sandwiched between the rotatable cutting bit and the bit holder. If the amount of contaminants or debris became too great, it impeded the rotation of the cutting bit. Despite prior art designs to allow free rotation, certain cutting applications such as asphalt milling and the continuous mining of coal cause tool rotation to be inhibited by fines accumulating between the mating surfaces of the tool holder and cutter tool. Once the accumulated fines become tightly packed between the tool retainer and the tool body and/or between the tool shoulder and the holder face, rotation is greatly reduced. Following reduced rotation, a wear flat will develop on the hard tip of the tool progressing down onto the steel body. After developing a wear flat, the tool rotation generally stops, whereby the remaining useful tool life is lost.
During the operation of the earlier cutting bits, the support block experienced wear due to the contact and rotation between the cutting bit and the support block, as well as the impingement of the debris from the cutting operation. In other prior art, such as U.S. Pat. Nos. 6,113,195 and 4,818,027, which incorporate a washer between the cutting bit and support block, the wear to the bit support block is reduced, however, during operation of said prior art and the holding element washer does not remain in a fixed position on the top face of the bit block. The holding washer elements in said prior art have a tendency to rotate on the top face of the bit block due to the contact between the washer and rotating cutter bit.
While the cutting bit was replaced on a periodic basis after the expiration of the useful life thereof, the support block was typically intended to be functional much longer than the cutting bit. As the bore and front face of the support block became worn, the support block lost its effectiveness due to deformation and wear of the bore and the front face thereof. In the case of the bore, it lost its initial cylindrical shape by becoming out-of-round, oversized or bell-mouthed. In the case of the front face of the support block, it lost its flatness. Each one of these conditions impeded the satisfactory rotation of the cutting bit in the support block.
In U.S. Pat. No. 5,931,542 to Britzke et al., the cutter bit assembly was designed to prevent rotation of the washer. The cutter bit assembly in Britzke et al. includes a substantially circular wear washer having a radially inwardly directed key. The wear washer key is adapted to fit within the retainer sleeve slot, thereby interlocking the retainer sleeve with the wear washer. This provided the benefit of greatly reducing wear on the top face of the bit block. This prior art design required additional cold work machining of the block and of the washer to form the key. In the field, upon insertion into the bit block, the washer key often became broken off in use or knocked out of its cooperating keyway groove so that the washer would not be fixed in position.
It is, therefore, apparent that in light of the past experience of earlier cutting bits, it would be beneficial to provide a rotatable cutting bit which has an improved ability to freely rotate during operation.
It would, therefore, be very advantageous to provide a cutting bit, which, during operation, protects the bore of the bit holder, as well as the front face of the support block, from deformation. By providing this protection, a cutting bit would help prolong the useful life of the support block, as well as help the rotation of the cutting bit.
It is an object of the invention to provide a rotatable cutting bit, and rotatable cutting bit-bit holder assembly and washer that have improved wear resistance characteristics.
It is an object of the invention to provide a rotatable cutting bit, and rotatable cutting bit-bit holder assembly, that has improved rotational characteristics between the cutter bit and top surface of the washer during operation.
An object of the present invention is to provide an efficient means for protecting holding support blocks, of the type used to hold cutting bits used in pulverizer and rotary drum or wheel machines, from excessive abrasion and impact damage. It is believed that the relative rotation between the rear face of the washer and front of the block face is reduced in the present invention.
The improved wear resistance properties of the invention reduce the amount of necessary maintenance of rotary drums in the field, resulting in reduced downtime and increased productivity. The invention is also simple to manufacture in a cost effective manner and easy to assemble in the field.